Description Neotrypaea californiensis (formerly Callianassa californiensis), the Bay ghost shrimp, is a species of ghost shrimp that lives on the Pacific coast of North America. It is a pale animal which grows to a length of 11.5 cm (4.5 in). One claw is bigger than the other, especially in males, and the enlarged claw is thought to have a function in mating. It is a deposit feeder that lives in extensive burrow systems, and is responsible for high rates of bioturbation. N. californiensis adversely affects oyster farms, and its numbers are controlled in some places by the application of pesticides. It carries out an important role in the ecosystem, and is used by fishermen as bait.

Neotrypaea californiensis reaches a length of 11.5 centimetres (4.5 in). The body is creamy-white, with patches of pale colour (pink, yellow or orange) on the appendages, and a pink abdomen.

Adult N. californiensis have one claw larger than the other, and in the males, the "master claw" can make up as much as 25% of the animal's mass – compared to only 10% in females – with the minor claw making up around 3% of the total body mass in both sexes. The enlarged claw is equally likely to be on the right side or the left side. The male's larger claw is thought to be used in agonistic encounters or during mating, and may be the result of sexual selection.

Eggs are laid in spring or early summer, and the larvae hatch in summer, living as plankton. They settle to the sea floor again as post-larvae in the late summer and fall.